Get which screen the cursor is in?
It's all accessible through bpy.context. The active area is accessible through context.area (of type Area), while data specific to the active area's current display type through context.space_data (of type Space).

Once the active space is ascertained as a 3D View, we can access its view properties through context.region_data or context.space_data.region_3d (of type RegionView3D) e.g. to check its view perspective.